1. Field of the Invention
The invention concerns adhesive compositions based on aqueous polychloroprene dispersions, a process for their production and their use as contact adhesives for inorganic or organic substrates.
2. Description of the Prior Art
Polychloroprene production has long been known; it is performed by emulsion polymerisation in an alkaline aqueous medium, cf. “Ullmanns Encyclopädie der technischen Chemie”, Vol. 9, p. 366, Verlag Urban und Schwarzenberg, Munich-Berlin 1957; “Encyclopedia of Polymer Science and Technology”, Vol. 3, p. 705-730, John Wiley, New York 1965; “Methoden der Organischen Chemie” (Houben-Weyl) XIV/1,738 f, Georg Thieme Verlag Stuttgart 1961.
Contact adhesives based on polychloroprene are mainly solvent-containing adhesives which are first applied to both parts to be joined and allowed to dry. By subsequently joining the two parts under pressure, a join is obtained with a high green strength. This green strength can be increased significantly by the addition of chlorine rubber. In the case of substances that are difficult to bond, such as plasticised PVC, adequate adhesion using polychloroprene contact adhesives can only be achieved after a graft reaction in solution, with methyl methacrylate for example.
For ecological and economic reasons there is a growing demand for suitable aqueous polychloroprene dispersions which can be processed to form corresponding aqueous adhesive formulations. The disadvantage here, however, is that after evaporation of the water the green strength—in comparison to solvent-containing adhesives—is lower. Although polychloroprene dispersions modified with carboxyl or acrylate groups have improved adhesion on various substrates, their green strength is no greater, especially on substrates that are difficult to bond, such as plasticised PVC.
The object of the present invention was therefore to provide an aqueous adhesive composition which after application to the substrates to be bonded and after subsequent joining thereof has a high green strength, especially on substrates that are difficult to bond.